Light-emitting device

ABSTRACT

A light-emitting device is disclosed capable of reducing the variation of an emission spectrum depending on an angle of viewing a light extraction surface. More particularly, a light-emitting device is disclosed capable of preventing impurities from dispersing from a light-emitting element into a thin film transistor as well as reducing the variation of an emission spectrum depending on an angle of viewing a light extraction surface. The disclosed light-emitting device comprises a substrate; a first insulating layer provided over the substrate; a transistor provided over the first insulating layer; and a second insulating layer having a first opening portion so that the transistor is covered and the substrate is exposed; wherein a light-emitting element is provided inside the first opening portion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an active matrix light-emitting device,and more particularly, a structure of a portion for extracting light.

2. Related Art

A light-emitting device utilizing light from an electroluminescentelement (light-emitting element) has attracted attention as a low powerconsumption display device having a wide viewing angle.

As a driving method for a light-emitting device that is used mainly as adisplay device, an active matrix driving method and a passive matrixdriving method can be used. An active matrix light-emitting device cancontrol emission and non-emission of every light-emitting element.Therefore, an active matrix light-emitting device can operate with lowerpower consumption than that of a passive matrix light-emitting device.The active matrix light-emitting device is suitable for mounting to notonly a display portion of a small electric appliance such as a cellularphone but also a display portion of a large TV set.

In an active matrix light-emitting device, a circuit for controlling thedrive of each light-emitting element is provided to each of thelight-emitting element. The circuit and the light-emitting element areprovided over a substrate so that extraction of light to the exterior isnot prevented by the circuit. A portion overlapped with thelight-emitting element is provided with a laminated insulating layerhaving a light transmitting property. Light is emitted outside bypassing through the insulating layer. The insulating layer is providedto form a circuit element such as a transistor or a capacitor element,each of which is a component of the circuit; or a wiring.

When light passes through the laminated insulating layer, light emissionmay multiply interacted with each other due to the difference ofrefractive index of each the insulating layer. As a result, an emissionspectrum is varied depending on an angle of viewing a light extractionsurface, which leads to a problem of deterioration of visibility of animage displayed on the light-emitting device.

The deterioration of visibility of an image due to the difference ofrefractive index of each layer may be occurred in a passive matrixlight-emitting device. For example, Unexamined Patent Publication No.7-211458 disclosed a light-emitting element with an improved structureto solve a problem of deterioration of visibility of an image caused bythe reflection of external light and light emission at an interface dueto the difference of refractive index of each layer composing alight-emitting element.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a light-emittingdevice capable of reducing the variation of an emission spectrumdepending on an angle of viewing a light extraction surface. It is morespecific object of the present invention to provide a light-emittingdevice capable of preventing impurities from dispersing from alight-emitting element into a thin film transistor as well as reducingthe variation of an emission spectrum depending on an angle of viewing alight extraction surface.

The present invention provides a light-emitting device comprising asubstrate; a first insulating layer provided over the substrate; atransistor provided over the first insulating layer; and a secondinsulating layer provided with a first opening portion so that thetransistor is covered and the substrate is exposed; wherein alight-emitting element is provided inside the first opening portion.

The transistor and the light-emitting element are electrically connectedwith each other via a connecting portion. The connecting portion isconnected to the transistor by passing through a contact hole thatpenetrates into the second insulating layer.

The second insulating layer may be a single layer or multiple layers ofa plurality layers made from different materials, preferably, a layermade from silicon oxide containing oxygen.

The present invention provides a light-emitting device comprising asubstrate; a first insulating layer provided over the substrate; atransistor provided over the first insulating layer; and a secondinsulating layer provided with a first opening portion so that thetransistor is covered and the substrate is exposed; wherein a firstelectrode, a light-emitting layer, and a second electrode aresequentially stacked over the substrate inside the first openingportion.

The transistor and the light-emitting element are electrically connectedwith each other via a connecting portion. The connecting portion isconnected to the transistor by passing through a contact hole thatpenetrates into the second insulating layer.

The second insulating layer may be a single layer or multiple layersmade from different materials, preferably, a layer made from siliconoxide containing oxygen.

The present invention provides a light-emitting device comprising asubstrate; a first insulating layer provided over the substrate; atransistor provided over the first insulating layer; a second insulatinglayer provided with a first opening portion so that the transistor iscovered and the substrate is exposed; and a third insulating layer forcovering the first opening portion and the second insulating layer;wherein a first electrode, a light-emitting layer, and a secondelectrode are sequentially stacked over the substrate inside the firstopening portion.

The transistor and the light-emitting element are electrically connectedwith each other via a connecting portion. The connecting portion isconnected to the transistor by passing through a contact hole thatpenetrates into the second insulating layer.

The second insulating layer may be a single layer or multiple layersmade from different materials, preferably, a layer made from siliconoxide containing oxygen. The third layer is preferably made from siliconnitride containing oxygen.

The present invention provides a light-emitting device comprising asubstrate; a first insulating layer provided over the substrate; atransistor provided over the first insulating layer; a second insulatinglayer provided with a first opening portion so that the transistor iscovered and the substrate is exposed; a first electrode for covering thefirst opening portion; a bank layer provided with a second openingportion so that the first electrode is exposed; a light-emitting layerprovided over the first electrode in the second opening portion; and asecond electrode provided over the light-emitting layer.

The transistor and the light-emitting element are electrically connectedwith each other via a connecting portion. The connecting portion isconnected to the transistor by passing through a contact hole thatpenetrates into the second insulating layer.

The second insulating layer may be a single layer or multiple layersmade from different materials, preferably, a layer made from siliconoxide containing oxygen. The third layer is preferably made from siliconnitride containing oxygen.

According to the present invention, a light-emitting device with reducedvariation of an emission spectrum depending on an angle of viewing alight extraction surface can be obtained.

By reducing the variation of an emission spectrum depending on an angleof viewing a light extraction surface, a display device and the likethat can provide an image having good visibility can be obtained.

These and other objects, features and advantages of the presentinvention will become more apparent upon reading of the followingdetailed description along with the accompanied drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory cross-sectional view of a structure of alight-emitting device according to the present invention;

FIG. 2 is an explanatory top view of a structure of a light-emittingdevice according to the present invention;

FIGS. 3A to 3E are explanatory views of a method for manufacturing alight-emitting device according to the present invention;

FIGS. 4A to 4C are explanatory views of a method for manufacturing alight-emitting device according to the present invention;

FIG. 5 is an explanatory view of a circuit for operating alight-emitting device according to the present invention;

FIG. 6 is an explanatory view of a circuit for operating alight-emitting device according to the present invention;

FIG. 7 is an explanatory top view of a light-emitting device accordingto the present invention after being sealed;

FIG. 8 is an explanatory cross-sectional view of a light-emitting deviceaccording to the present invention after being sealed; and

FIGS. 9A to 9C are explanatory views of electric appliances practicingthe present invention.

DESCRIPTION OF THE INVENTION Embodiment 1

A light-emitting device according to the present invention is explainedwith reference to FIG. 1.

An insulating layer 12 formed by two layers of an insulating layer 12 aand an insulating layer 12 b is provided over a substrate 11. Astaggered transistor 16 including a semiconductor layer 13, a gateinsulating layer 14 and a gate electrode 15 is provided over theinsulating layer 12 b.

The transistor 16 is covered by an insulating layer 17 having a firstopening portion. The insulating layer 17 is formed by, but notexclusively, two layers of an insulating layer 17 a (lower layer) and aninsulating layer 17 b (upper layer). The insulating layer 17 may beformed by a single layer or three or more layers. Further, the firstopening portion penetrates into the gate insulating layer 14 and theinsulating layer 12 to reach the substrate 11. Therefore, a part of thesubstrate 11 is exposed from the first opening portion.

The insulating layer 17 and the first opening portion are covered by aninsulating layer 18. Inside the first opening portion, the insulatinglayer 18 and the substrate 11 are overlapped to be in contact with eachother.

A light-emitting element 24 is composed of a first electrode 20, asecond electrode 23, and a light-emitting layer 22 interposed betweenthese electrodes; and is provided over the insulating layer 18. Thefirst electrode 20 and the insulating layer 18 are overlapped to be incontact with each other.

The transistor 16 is electrically connected to the light-emittingelement 24 via a connecting portion 19 a made from a conductor. Theconnecting portion 19 a is provided over the insulating layer 18 to bereached the semiconductor layer 13 by passing through a contact holethat penetrates into the insulating layers 17 and 18. The connectingportion 19 a is electrically connected to the first electrode 20 bybeing a part of the connecting portion 19 a in contact with the firstelectrode 20.

The connecting portion 19 a, a wiring 19 b, the insulating layer 18, andthe like are covered by a bank layer 21 having a second opening portionthat is provided to expose a part of the first electrode 20. In thesecond opening portion, the light-emitting layer 22 is provided over thefirst electrode 20 and the second electrode 23 is provided over thelight-emitting layer 22. The laminated portion of the first electrode20, the light-emitting layer 22, and the second electrode 23 serve asthe light-emitting element 24. Further, the light-emitting layer 22 isformed by a single layer or multiple layers containing a light-emittingmaterial.

In this embodiment, the substrate 11 is formed by a material transparentto visible light such as glass. Besides, resin having flexibility suchas plastic can be used as the substrate 11. Alternatively, any materialcan be used as the substrate 11, as long as it has a light transmittingproperty and serves as a support medium for supporting the transistor 16or the light-emitting element 24.

The insulating layer 12 a and the insulating layer 12 b are made of amaterial that can prevent impurities from dispersing from the substrate11. Especially, the insulating layer 12 a is preferably a layer having afunction of preventing impurities from dispersing. Further, theinsulating layer 12 b is preferably a layer having a small stressdifference from that of the semiconductor layer 13 as well as having afunction of preventing impurities from dispersing. As such the layers, alayer made from silicon oxide can be used. The layer made from thesilicon oxide may contain nitrogen of several % or less. The insulatinglayer 12 is not always required to be formed by two layers. In the casethat impurities can be prevented from dispersing from the substrate 11by providing only the insulating layer 12 a, the insulating layer 12 bis not always required to be provided between the semiconductor layer 13and the insulating layer 12 a.

The insulating layer 17 a is preferably made from silicon nitridecapable of being detected to contain an oxygen element of from 5 to 6%by Rutherford Backscattering Spectrometry/Hydrogen Forward scatteringSpectrometry (RBS/HFS). Hydrogen is included in such the layer.Accordingly, hydrogen treatment can be carried out by using thehydrogen. Further, the layer serves to prevent impurities fromdispersing into the transistor.

The insulating layer 18 is preferably made from a material having lowmoisture permeability, higher refractive index than that of thesubstrate 11, and lower refractive index than that of the firstelectrode 20. Especially, the insulating layer 18 is preferably madefrom silicon nitride capable of being detected to contain an oxygenelement of from 5 to 6% by Rutherford BackscatteringSpectrometry/Hydrogen Forward scattering Spectrometry (RBS/HFS). Suchthe layer has high blocking capability of impurities and is hardlypermeable to moisture. Accordingly, the impurities can be prevented fromdispersing from the light-emitting element 24 into the transistor 16. Inthe case that the insulating layer 17 is made from a material havinghigh moisture permeability, the layer can serve to prevent moisture frompenetrating into the light-emitting element 24 via the insulating layer17. When there is no problem of moisture penetration into thelight-emitting element, the insulating layer 18 is not always requiredto be provided.

Further, the first electrode 20 may be made from a conductor transparentto visible light such as indium tin oxide (ITO), ITO containing siliconoxide, indium zinc oxide (IZO) that is a mixture of indium oxide and 2to 20% of zinc oxide (ZnO), or the like.

The insulating layer 17 b may be multiple layers or a single layer. Theinsulating layer 17 b may be made from either an inorganic material suchas silicon oxide, siloxane, or silicon nitride; or an organic materialsuch as acrylic or polyimide. Alternatively, the insulating layer 17 bmay be made from both of the inorganic and organic materials. At anyrate, the insulating layer 17 b may be an insulator. The insulatinglayer 17 b preferably includes a layer made from a material having aself-smoothness property such as siloxane or acrylic to smooth thesurface of the insulating layer 18. The surface of the insulating layer17 b may be smoothed by not only utilizing a material having aself-smoothness property but also polishing.

The light-emitting layer 22 may be made from either an organic materialor an inorganic material. Alternatively, the light-emitting layer 22 maybe made from both of an organic material and an inorganic material.

In the light-emitting device according to the present invention, thestructure of the transistor 16 is not especially limited. The transistor16 may be either a single gate transistor or a multi-gate transistor.Alternatively, the transistor 16 may have a single drain structure, anLDD (Lightly Doped Drain) structure, or a structure formed byoverlapping an LDD region and a gate electrode.

FIG. 2 is a top view of the light-emitting device according to thepresent invention. The cross-sectional view of FIG. 1 illustrates a partof the cross-section of FIG. 2 taken along line of A-A′. Therefore, likecomponents in FIG. 2 are denoted by like numerals as of FIG. 1. That is,reference numeral 13 denotes a semiconductor layer; 15, a gateelectrode; 19 b, a wiring; 19 a, a connecting portion; 20, a firstelectrode; and 21, a bank layer. Although not shown in FIG. 1, referencenumerals 19 c, 29 a, and 29 b denote wirings; and 27 and 28 denotetransistors.

In the foregoing light-emitting device, light from the light-emittingelement 24 is emitted outside by passing through sequentially the firstelectrode 20, the insulating layer 18, and the substrate 11.

In the foregoing light-emitting device, light reflection duringextracting light outside the light-emitting device can be reduced, andimpurities can be sufficiently prevented from dispersing into thetransistor from the substrate. Moreover, in the foregoing light-emittingdevice, multiple interaction due to reflection light can be restrictedby reducing light reflection during extracting light outside. As aresult of restricting the multiple interaction, the variation of anemission spectrum depending on an angle of viewing a light extractionsurface can be decreased. Accordingly, the visibility of an imagedisplayed on the light-emitting device can be improved.

Embodiment 2

In this embodiment, a method for manufacturing a light-emitting deviceillustrated in FIGS. 1 and 2 is explained with reference to FIGS. 3A to4C.

Insulating layers 12 a and 12 b are stacked over a substrate 11, and asemiconductor layer 13 is stacked over the insulating layer 12 b.

The semiconductor layer 13 is processed into a desired form. Thesemiconductor layer 13 may be processed by etching with a resist mask.

A gate insulating layer 14 for covering the semiconductor layer 13, theinsulating layer 12 b, and the like, is formed, and a conductive layeris stacked over the gate insulating layer 14.

The conductive layer is processed into a desired form to form a gateelectrode 15. Here, wirings 29 a and 29 b (FIG. 2) are formed as well asthe gate electrode 15 is formed. The conductive layer may be processedby etching using a resist mask.

High concentrations of impurities are doped to the semiconductor layer13 using the gate electrode 15 as a mask. Accordingly, a transistor 16including the semiconductor layer 13, the gate insulating layer 14, andthe gate electrode 15 can be manufactured.

The manufacturing process of the transistor 16 is not especially limitedand may be modified appropriately to manufacture the transistor having adesired structure.

An insulating layer 17 a that covers the gate electrode 15, the wirings29 a, 29 b, the gate insulating layer 14, and the like is formed. Inthis embodiment, the insulating layer 17 a is preferably made fromsilicon nitride capable of being detected to contain an oxygen elementof from 5 to 6% by Rutherford Backscattering Spectrometry/HydrogenForward scattering Spectrometry (RBS/HFS). The layer made from siliconnitride containing an oxygen element of from 5 to 6% can be formed byusing mixed gas as a raw material of monosilane (SiH₄), ammonia (NH₃),dinitrogen monoxide (N₂O), and hydrogen (H₂) having respectively a flowratio of 1:10:2:40 by plasma CVD.

An insulating layer 17 b that covers the insulating layer 17 a isformed. In this embodiment, the insulating layer 17 b is, but notexclusively, made from an inorganic material having a self-smoothnessproperty such as siloxane. The insulating layer 17 b may be made from anorganic material having a self-smoothness property. Further, theinsulating layer 17 b is not always required to be made from a materialhaving a self-smoothness property. The insulating layer 17 b may be madefrom only a material with no self-smoothness property (FIG. 3A).

A first opening portion that penetrates the insulating layer 17 to reachthe substrate 11 is formed by etching the insulating layer 17 formed bythe insulating layers 17 a and 17 b and the like. Accordingly, thesubstrate 11 is exposed from the first opening portion (FIG. 3B).

An insulating layer 18 that covers the first opening portion and theinsulating layer 17 is formed. In this embodiment, the insulating layer17 a is made from silicon nitride capable of being detected to containan oxygen element of from 5 to 6% by Rutherford BackscatteringSpectrometry/Hydrogen Forward scattering Spectrometry (RBS/HFS) (FIG.3C).

Heat treatment is performed at a temperature of from 350 to 500° C.Accordingly, hydrogen contained in the insulating layer 17 and the likeis dispersed, which leads to the hydrogenation of the transistor 16.This process can be performed after forming the insulating layer 17 aand before forming the insulating layer 17 b (FIG. 3D).

A conductive layer 19 that covers the insulating layer 18 and the likeis formed (FIG. 3E). Then, the conductive layer 19 is processed intodesired forms to form a connecting portion 19 a, wirings 19 b, 19 c, afilm 19 d, and the like so that the substrate 11 is exposed from thefirst opening portion (FIG. 4A).

A conductive layer having a light transmitting property is formed insuch a way that the connecting portion 19 a and the like are covered bythe conductive layer. Then, the conductive layer is processed to form afirst electrode 20. In this embodiment, the first electrode 20 isprocessed to be partly in contact with the connecting portion 19 a, andto cover an opening portion provided to the insulating layer 18. Here,the first electrode 20 is in contact with the substrate 11 via theinsulating layer 18 (FIG. 4B).

A bank layer 21 that has an opening portion to expose a part of thefirst electrode 20 and that covers the connecting portion 19 a, theinsulating layer 18, and the like is formed. The bank layer 21 may beformed by processing a photosensitive resin material into a desired formby exposure and development. Alternatively, the bank layer 21 may beformed by forming a layer made from a nonphotosensitive inorganicmaterial or organic material, and etching to be processed into a desiredform.

A light-emitting layer 22 that covers the first electrode 20 exposedfrom the bank layer 21 is formed. The light-emitting layer 22 may beformed by any one of vapor deposition, ink jetting, spin coating, or thelike. In the case that the surface of the substrate 11 hasirregularities, the irregularities can be relieved by providing a layermade from a high molecular material that is a mixture of poly(styrenesulfone) (PSS) and poly(ethylene dioxythiophene) (PEDOT) to a part ofthe light-emitting layer 22. A second electrode 23 that covers thelight-emitting layer 22 is formed. Accordingly, a light-emitting element24 composed of the first electrode 20, the light-emitting layer 22, andthe second electrode 23 is formed.

EXAMPLE 1

A light-emitting device according to the present invention is describedin this example. Further, the structure of the light-emitting deviceaccording to the present invention, the material for constructing thelight-emitting device according to the present invention, and the likeare not limited to those explained in this example.

A light-emitting device according to this example is a light-emittingdevice according to the present invention having the cross-sectionalstructure as illustrated in FIG. 1.

In this example, a light-emitting layer 22 that is a component of alight-emitting element 24 is composed of a plurality of layers. Theplurality of layers are formed by combining a plurality of layers, eachof which is made from a material selected from the group consisting of amaterial having a high carrier transporting property or a materialhaving a high carrier injecting property. The plurality of layerscontains partly a material having a high light-emitting property. Amaterial for forming the light-emitting layer 22 may be either aninorganic material or an organic material. In the case of using anorganic material, either of a low molecular organic material or a highmolecular organic material can be used.

As a light-emitting material,4-dicyanomethylene-2-methyl-6-[2-(1,1,7,7-tetramethyljulolidine-9-yl)ethenyl]-4H-pyran(abbreviated DCJT),4-dicyanomethylene-2-t-butyl-6-[2-(1,1,7,7-tetramethyljulolidine-9-yl)ethenyl]-4H-pyran(abbreviated DPA), periflanthene,2,5-dicyano-1,4-bis[2-(10-methoxy-1,1,7,7-tetramethyljulolidine-9-yl)ethenyl]benzene,N,N′-dimethylquinacridone (abbreviated DMQd), coumarin 6, coumarin 545T,tris(8-quinolinolato)aluminum (abbreviated Alq₃), 9,9′-biantrile,9,10-diphenylantracene (abbreviated DPA), 9,10-bis(2-naphtyl)anthracene(abbreviated DNA), or the like can be used. Another material may beused.

Besides the foregoing singlet excited light-emitting material, a tripletexcited material containing a metal complex or the like can be used. Forexample, among a red emitting pixel, a green emitting pixel, and a blueemitting pixel; a red emitting pixel having comparative shorthalf-brightness life is formed by a triplet excited light-emittingmaterial and the other are formed by singlet excited light-emittingmaterials. The triplet excited light-emitting material has acharacteristic that it requires lower power consumption than that of thesinglet excited light-emitting material to obtain a certain level ofluminance since the triplet excited light-emitting material has highluminous efficiency. In the case that the triplet excited light-emittingmaterial is used for forming the red emitting pixel, the reliability canbe improved since the light-emitting element requires a small amount ofcurrent. To reduce power consumption, the red emitting pixel and thegreen emitting pixel may be formed by the triplet excited light-emittingmaterial, and the blue emitting pixel may be formed by a single excitedlight-emitting material. The power consumption of a green light-emittingelement that has high visibility for human can be reduced by using thetriplet excited light-emitting material for forming the greenlight-emitting element.

As an example for the triplet excited light-emitting material, amaterial using a metal complex as a dopant such as a metal complexincluding platinum that is the third transition element as a centralmetal or a metal complex including iridium as a central metal is wellknown. The triplet excited light-emitting material is not limited tothese compounds. A compound that has the foregoing structure and thathas an element belonging 8 to 10 groups in the periodic table as acentral metal can be used.

As a material having a high carrier transporting property, especially, amaterial having a high electron transporting property, for example, ametal complex or the like having a quinoline skeleton or abenzoquinoline skeleton such as tris(8-quinolinolate) aluminum(abbreviated Alq₃), tris(5-methyl-8-quinolinolate) aluminum (abbreviatedAlmq₃), bis(10-hydroxybenzo[h]-quinolinato) beryllium (abbreviatedBeBq₂), or bis(2-methyl-8-quinolinolato)-4-phenylphenolato-aluminum(abbreviated BAlq). As a material having a high hole transportingproperty, for example, aromatic amine (that is, the one having a benzenering-nitrogen bond) based compounds such as4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (abbreviated α-NPD),4,4′-bis[N-(3-methylphenyl)-N-phenyl-amino]-biphenyl (abbreviated TPD),4,4′,4″-tris(N,N-diphenyl-amino)-triphenyl amine (abbreviated TDATA),and 4,4′,4″-tris[N-(3-methylphenyl)-N-phenyl-amino]-triphenylamine(abbreviated MTDATA) can be nominated. As a material having a highcarrier injecting property, especially, a material having a highelectron injecting property, a compound of an alkali metal or an alkaliearth metal such as lithium fluoride (LiF), cesium fluoride (CsF),calcium fluoride (CaF₂), or the like can be nominated. Besides, amixture of a material having a high electron transportation propertysuch as Alq₃ and an alkali earth metal such as magnesium (Mg). As amaterial having a high hole injecting property, for example, metal oxidesuch as molybdenum oxide (MoOx), vanadium oxide (VOx), ruthenium oxide(RuOx), tungsten oxide (WOx), manganese oxide (MnOx), or the like can benominated. Besides, a phthalocyanine compound such as phthalocyanine(abbreviated H₂Pc) or copper phthalocyanine (CuPc) can be nominated. Ahigh molecular material or the like that is a mixture of poly(ethylenedioxythiophene) (PEDOT) and poly(styrene sulfone) (PSS) having a highhole injecting property and a high hole transportation property can beused.

A high molecular organic light-emitting material has higher physicalstrength than that of a low molecular organic light-emitting material,and so a light-emitting element can be manufactured to have highdurability. A light-emitting element can be comparatively readilymanufactured since a light-emitting layer can be formed by coating.

A transistor 16 is a staggered TFT. Alternatively, the transistor 16 maybe a reverse staggered TFT. Further, in the case of using the reversestaggered TFT, the transistor 16 may be a so-called channel protectiveTFT provided with a protective layer over a semiconductor layer or aso-called channel etching TFT provided with a partly etchedsemiconductor layer.

A semiconductor layer 13 may be either of a crystalline semiconductorlayer or an amorphous semiconductor layer. Alternatively, thesemiconductor layer 13 may be a semiamorphous semiconductor layer.

The semiamorphous semiconductor has an intermediate structure between anamorphous structure and a crystalline structure (including singlecrystals and poly crystals). The semiamorphous semiconductor has astable third state with respect to free energy, and a crystalline regionhaving a short-range order and lattice distortion. At least a part ofthe semiconductor includes crystal grains with grain diameters of from0.5 to 20 nm. A raman spectrum is shifted to a lower wave number than520 cm⁻¹. By X-ray diffraction, diffraction peaks (111), (220) that maybe derived from a Si crystalline lattice are observed. Hydrogen orhalogen of 1 atomic % or more is contained in the semiamorphoussemiconductor as neutralizer for dangling bond. Such semiamorphoussemiconductor is referred to as what is called micro crystalsemiconductor. A silicide gas is used to be carried out with glowdischarge decomposition (plasma CVD). As the silicide gas, Si₂H₆,SiH₂Cl₂, SiHCl₃, SiCl₄, SiF₄, or the like in addition to SiH₄ can beused. The silicide gas can be diluted by H₂, or the H₂ and one or aplurality of rare gas elements selected from the group consisting of He,Ar, Kr, and Ne. The dilution rate is in the range of from 2 to 1000times. An applied voltage is in the range of from 0.1 to 133 Pa. A powersource frequency is in the range of from 1 to 120 MHz, preferably, 13 to60 MHz. A heat temperature for a substrate is at most 300° C.,preferably, 100 to 250° C. As impurity elements in the film, atmosphericconstituents such as oxygen, nitrogen, carbon, and the like havepreferably concentrations of 1×10²⁰/cm⁻¹ or less, especially, oxygenconcentration is 5×10¹⁹/cm³ or less, preferably, 1×10¹⁹/cm³ or less. ATFT (thin film transistor) including semiamorphous semiconductor hasmobility of approximately from 1 to 10 m²/Vsec.

As a specific example of a crystalline semiconductor layer, asemiconductor layer formed by single crystalline silicon,polycrystalline silicon, silicon germanium, or the like can benominated. These semiconductor layers may be formed by lasercrystallization, or crystallization by a solid phase growth method usingnickel or the like.

In the case that a semiconductor layer is formed by an amorphousmaterial, for example, amorphous silicon; a light-emitting device haspreferably a circuit composed of the transistor 16 and the othertransistors (for composing a circuit for driving a light-emittingelement), each of which is formed by an N-channel type transistor. Inthe case that a semiconductor layer is formed by other material than theamorphous material, a light-emitting device may have a circuit composedof either an N-channel type transistor or a P-channel type transistor;or a light-emitting device may have a circuit composed of both of theN-channel type transistor and the P-channel type transistor.

An edge portion of a bank layer 21 is preferably in the form of having aradius of curvature varying continuously as illustrated in FIG. 1. Thebank layer 21 is made from acrylic, siloxane (a substance which has askeleton formed by the bond of silicon (Si) and oxygen (O), and whichincludes at least hydrogen as a substituent), resist, silicon oxide, orthe like. The bank layer 21 may be formed by at least one of aninorganic film or an organic film, alternatively, both of the films.

A light-emitting element 24 may have the structure in which a firstelectrode 20 serves as an anode and a second electrode 23 serves as acathode, alternatively, the structure in which the first electrode 20serves as a cathode and a second electrode 23 serves as an anode.Further, the transistor 16 is a P-channel transistor in the case offorming the former structure, whereas the transistor 16 is an N-channeltransistor in the case of forming the latter structure.

A light-emitting device according to the present invention is composedof a plurality of pixels, each of which includes the foregoinglight-emitting element 24 and transistor 16, in a matrix configuration.A light-emitting layer may have the structure in which each oflight-emitting layers having different emission wavelength bands isrespectively provided to each pixel for color display. Typically,light-emitting layers corresponding to color of R (red), G (green), andB (blue) are formed. In this instance, color purity can be improved anda pixel portion can be prevented from being a mirror surface(reflection) by providing a filter (colored layer) transparent to lightin each emission wavelength region at the light emission side of thepixel. By providing the filter (colored layer), a circularly-polarizedlight plate or the like that is conventionally required becomes notrequired, further, light can be emitted from the light-emitting layerwithout loss of light. Moreover, color changes occurred in the case ofviewing obliquely the pixel portion (display screen) can be furtherreduced.

The light-emitting layer may have the structure of exhibiting mono coloremission or white emission to be used in color display, instead of thestructure of providing light-emitting layers corresponding to each coloras mentioned above. In the case of using a white light-emittingmaterial, color display can be realized by providing a filter (coloredlayer) transparent to light at a particular wavelength at a lightemission side of a pixel.

To form a light-emitting layer that exhibits white emission, forexample, Alq₃, Alq₃ partly doped with Nile red, p-EtTAZ, TPD (aromaticdiamine) are deposited sequentially by vapor deposition. In the casethat the light-emitting layer is formed by spin coating, the material ispreferably baked by vacuum heating after being coated. For example,poly(ethylene dioxythiophene)/poly(styrene sulfonate) solution(PEDOT/PSS) may be coated over a whole surface and baked, and a solutionof polyvinylcarbazole (PVK) doped with pigments(1,1,4,4-tetraphenyl-1,3-butadiene (abbreviated TPB),4-dicyanomethylene-2-methyl-6-(p-dimethylamino-styryl)-4H-pyran (DCM1),Nile red, coumarin 6, or the like) may be coated over a whole surfaceand baked.

The light-emitting layer may be formed by a single layer besides amultilayer as mentioned above. In this instance, the light-emittinglayer may be made from polyvinylcarbazole (PVK) dispersed with a1,3,4-oxadiazole derivative (PBD). Further, white emission can beobtained by dispersing PBD of 30 wt % and dispersing an appropriateamount of four kinds of pigments (TPB, coumarin 6, DCM1, and Nile red).

A light-emitting element that is a component of a light-emitting deviceaccording to the present invention emits light under forward bias. Apixel of a display device formed by using the light-emitting element candrive by an active matrix driving technique. At any rate, each pixel isemitted by applying forward bias at a specified timing. Further, therespective pixels are in non-emission state for a certain period. Thereliability of the light-emitting element can be improved by applyingreverse bias in the period in which the pixels are in the, non-emissionstate. The light-emitting element may be in deterioration mode oflowering emission intensity under a regular driving condition or may bein deterioration mode of lowering apparently luminance due to theexpansion of a non-emission region within the pixel. The deteriorationprogression can be delayed by AC drive of applying forward bias andreverse bias, which leads to the improvement of the reliability of thelight-emitting device.

The foregoing structure can be applied not only to the light-emittingdevice according to the present invention as illustrated in FIG. 1 butanother light-emitting device according to the present invention.

EXAMPLE 2

In this example, a circuit provided to a pixel portion for driving alight-emitting element in a light-emitting device according to thepresent invention is explained. Further, the circuit for driving thelight-emitting element is not limited to that explained in this example.

As illustrated in FIG. 5, a light-emitting element 301 is connected to acircuit for driving each light-emitting element. The circuit has adriving transistor 321 for determining emission or non-emission of thelight-emitting element 301 by an image signal, a switching transistor322 for controlling input of the image signal, and an erasing transistor323 for making the light-emitting element 301 be in a non-emission stateregardless of the image signal. A source (or drain) of the switchingtransistor 322 connects to a source signal line 331, a source of thedriving transistor 321 and a source of the erasing transistor 323connect to a current supply line 332 extending in parallel with thesource signal line 331, and a gate of the erasing transistor 323extending in parallel with a first scanning line 333 connects to asecond scanning line 334. Further, the driving transistor 321 connectsto in series with the light-emitting element 301.

A method for driving the light-emitting element 301 when thelight-emitting element 301 emits light is explained. Upon the firstscanning line 333 being selected in a write period, the switchingtransistor 322 whose gate is connected to the first scanning line 333 isturned ON. An image signal inputted to the source signal line 331 isinputted to a gate of the driving transistor 321 via the switchingtransistor 322. Then, current is flown from the current supply line 332to the light-emitting element 301, which leads to green emission, forexample. Luminance of the emission depends on an amount of the currentflow in the light-emitting element 301.

The light-emitting element 301 corresponds to a light-emitting element24 in FIG. 1, and the driving transistor 321 corresponds to a transistor16 in FIG. 1. The erasing transistor 323 corresponds to a transistor 28in FIG. 2, and the switching transistor 322 corresponds to a transistor27 in FIG. 2. Further, the source signal line 331 corresponds to awiring 19 c in FIG. 2, the current supply line 332 corresponds to 19 bin FIG. 2, the first scanning line 333 corresponds to a wiring 29 a inFIG. 2, and the second scanning line 334 corresponds to a wiring 29 b inFIG. 2.

The structure of the circuit connected to each light-emitting element isnot limited to that explained in this example. The circuit may haveother structure than the foregoing structure as illustrated in FIG. 6.

A circuit illustrated in FIG. 6 is then explained.

As illustrated in FIG. 6, a light-emitting element 801 is connected to acircuit for driving each light-emitting element. The circuit has adriving transistor 821 for determining emission or non-emission of thelight-emitting element 801 by an image signal, a switching transistor822 for controlling input of the image signal, an erasing transistor 823for making the light-emitting element 801 be in a non-emission stateregardless of the image signal, and a current controlling transistor 824for controlling an amount of current supplied to the light-emittingelement 801. A source (or drain) of the switching transistor 822connects to a source signal line 831, a source of the driving transistor821 and a source of the erasing transistor 823 connect to a currentsupply line 832 extending in parallel with the source signal line 831, agate of the switching transistor 822 connects to a first scanning line833, and a gate of the erasing transistor 823 extending in parallel witha first scanning line 833 connects to a second scanning line 834.Further, the driving transistor 821 connects to in series with thelight-emitting element 801 via the current controlling transistor 824. Agate of the current controlling transistor 824 connects to a powersource line 835. In addition, the current controlling transistor 824 isconstructed and controlled so that current flows in a saturation regionin voltage-current (Vd-Id) characteristics. Accordingly, an amount ofvalue of current flown in the current controlling transistor 824 can bedetermined.

A method for driving the light-emitting element 801 when thelight-emitting element 801 emits light is explained. Upon the firstscanning line 833 being selected in a write period, the switchingtransistor 822 whose gate is connected to the first scanning line 833 isturned ON. An image signal inputted to the source signal line 831 isinputted to a gate of the driving transistor 821 via the switchingtransistor 822. Further, current flows from the current supply line 832to the light-emitting element 801 via the driving transistor 821 and thecurrent controlling transistor 824 that becomes in ON state due to asignal from the power source line 835, which leads to light emission.The amount of current flown in the light-emitting element depends on thecurrent controlling transistor 824.

EXAMPLE 3

A light-emitting device according to the present invention can extractefficiently light from a light-emitting layer to the outside. Therefore,an electric appliance mounted with the light-emitting device accordingto the present invention requires a small amount of power for a displayfunction. Since the variation of an emission spectrum that depends on anangle of viewing a light extraction surface is small, the electricappliance mounted with the light-emitting device according to thepresent invention can obtain an image with favorable visibility.Hereinafter, an electric appliance and the like mounted with thelight-emitting device according to the present invention are explained.

A light-emitting device according to the present invention is mounted tovarious kinds of electric appliances after being installed and sealedwith an external input terminal.

In this example, a light-emitting device according to the presentinvention after sealing and electric appliances mounted with thelight-emitting device are explained with reference to FIGS. 7 to 9C.FIGS. 7 to 9C illustrate only one example and the structure of thelight-emitting device is not limited thereto.

A light-emitting device according to the present invention is explainedwith reference to FIGS. 7 and 8. FIG. 8 is a cross-sectional view ofFIG. 7.

As illustrated in FIG. 7, a pixel portion 502, driving circuit portions503, transistor 504 formed in the pixel portion 502, and a connectingterminal portion 505 are provided over a first substrate 501 formed by aglass. The driving circuit portions 503 is respectively provided alongedges of the pixel portion 502. The connecting terminal portion 505 isprovided adjacent to the driving circuit portion 503 to be connected tothe driving circuit portion 503 by a wiring. In this example, a glasssubstrate is used as the first substrate 501. Besides, a quartzsubstrate, a flexible substrate such as a plastic substrate, or the likecan be used.

The pixel portion 502 is provided with a light-emitting element and acircuit element (that is each portion unit for composing a circuit, forexample, transistor, resistance, and the like) for driving thelight-emitting element. FIG. 8 is a schematic view of a cross-sectionalstructure of the first substrate 501. The present invention is practicedin the pixel portion 502.

A material having a water absorbing property is secured to a secondsubstrate 511 provided opposite to the first substrate 501. In FIG. 8, aregion 512 to which the material having a water absorbing property issecured is provided to the outside of the pixel portion 502 and alongwith the edge of the pixel portion 502. In FIG. 7, the region 512 isoverlapped with the driving circuit portion 503 and the transistor 506.In this example, granular calcium oxide is used as the material having awater absorbing property. A concave portion is provided to a part of thesecond substrate 511 to secure the calcium oxide to the concave portionusing ester acrylate as fixative.

In this example, a glass substrate is used as the second substrate 511.Besides, a quartz substrate, a flexible substrate such as a plasticsubstrate, or the like can be used. A material having high moisturepermeability can be used as fixative instead of using the esteracrylate. An inorganic material such as siloxane can be used as fixativeother than resin. In this example, fixative is solidified by heating.Further, a material having high moisture permeability that includespolymerization initiator and is hardened by light can be used asfixative. In this example, granular calcium oxide is used as thematerial having a water adsorbing property, but not exclusively, anothermaterial having a water adsorbing property can be used. Alternatively, acomposite formed by molecules having water adsorbing property bychemical adsorption mixed in organic solvent, which is injected into theconcave portion and solidified, can be used.

The first substrate 501 and second substrate 511 are pasted to eachother by sealant 522 so that the light-emitting element, transistor, andthe like are sealed inside these substrates. A flexible printed wiringboard (FPC) 523 is connected to the driving circuit portion 503 and thelike via the connecting terminal portion 505.

Space (inside the light-emitting device) surrounded by the firstsubstrate 501, the second substrate 511, and the sealant 522 is filledwith an inert gas such as nitrogen. The space surrounded by the firstsubstrate 501, the second substrate 511, and the sealant 522 may befilled with a resin material instead of gas as in this example. A layeror multiple layers for preventing moisture from penetrating into thespace may be provided over the side provided to the material having awater absorbing property of the second substrate 511.

Since there is no obstruction of light extraction from the pixel portion502 to the outside in the above described light-emitting deviceaccording to the present invention, the light-emitting device can beused effectively in the case of extracting light from the secondelectrode (that is provided opposite to a substrate via a light-emittinglayer) of the light-emitting element. Further, since the material havinga water absorbing property is secured in the region 512, the materialhaving a water absorbing property will not be in contact with thedriving circuit portion 503 and the transistor 506 even if the firstsubstrate 501 and the second substrate 511 are pressed to be pasted toeach other. Accordingly, the material having a water absorbing propertycan prevent the driving circuit portion 503 and the transistor 506 frombeing damaged.

FIGS. 9A to 9C illustrate one embodiment of electric appliances mountedwith the light-emitting device according to the present invention.

FIG. 9A illustrates a personal computer manufactured by practicing thepresent invention composed of a main body 5521, a housing 5522, adisplay portion 5523, a key board 5524, and the like. The personalcomputer can be completed by incorporating a light-emitting devicehaving a light-emitting element according to the present invention as adisplay portion.

FIG. 9B illustrates a cellular phone manufactured by practicing thepresent invention composed of a main body 5552, a display portion 5551,a sound output portion 5554, a sound input portion 5555, operationswitches 5556, 5557, an antenna 5553, and the like. The cellular phonecan be completed by incorporating a light-emitting device having alight-emitting element according to the present invention as a displayportion.

FIG. 9C illustrates a television set manufactured by practicing thepresent invention composed of a display portion 5531, a housing 5532, aspeaker 5533, and the like. The television set can be completed byincorporating a light-emitting device having a light-emitting elementaccording to the present invention as a display portion.

As noted above, the light-emitting device according to the presentinvention is extremely suitable to be used as a display portion ofvarious kinds of electric appliances.

A personal computer is explained in this example. Besides, alight-emitting device having a light-emitting element according to thepresent invention may be mounted to a car navigation system, a lightingsystem, and the like.

Although the present invention has been fully described by way ofexamples with reference to the accompanying drawings, it is to beunderstood that various changes and modifications will be apparent tothose skilled in the art. Therefore, unless otherwise such changes andmodifications depart from the scope of the present invention hereinafterdescribed, they should be construed as being included therein.

1. A light-emitting device comprising: a first substrate; alight-emitting element over the first substrate; a second substrate overthe light-emitting element, wherein the second substrate contains aconcave portion; a sealant between the first substrate and the secondsubstrate; and a material having a water absorbing property formed inthe concave portion, wherein the material having the water absorbingproperty is provided so as to be spaced from the sealant.
 2. Alight-emitting device according to claim 1, wherein at least one of thefirst substrate and the second substrate contains a plastic.
 3. Alight-emitting device according to claim 1, wherein the material havingthe water absorbing property contains calcium oxide.
 4. A light-emittingdevice according to claim 1, wherein the light-emitting device isincorporated in one selected from the group consisting of a personalcomputer, a cellular phone, a television set, a navigation system, and alighting system.
 5. A light-emitting device comprising: a firstsubstrate; a light-emitting element over the first substrate; a secondsubstrate over the light-emitting element, wherein the second substratecontains a concave portion; a sealant between the first substrate andthe second substrate; and a material having a water absorbing propertyformed in the concave portion, wherein the material having the waterabsorbing property is provided so as not to overlap the light-emittingelement, and so as to be spaced from the sealant.
 6. A light-emittingdevice according to claim 5, wherein at least one of the first substrateand the second substrate contains a plastic.
 7. A light-emitting deviceaccording to claim 5, wherein the material having the water absorbingproperty contains calcium oxide.
 8. A light-emitting device according toclaim 5, wherein the display device is incorporated in one selected fromthe group consisting of a personal computer, a cellular phone, atelevision set, a navigation system, and a lighting system.
 9. Alight-emitting device comprising: a first substrate; a light-emittingelement over the first substrate; a second substrate over thelight-emitting element, wherein the second substrate contains a concaveportion; a sealant between the first substrate and the second substrate;and a material having a water absorbing property formed in the concaveportion, wherein the material having the water absorbing property isprovided so as to surround a periphery of the light-emitting element,and so as to be spaced from the sealant.
 10. A light-emitting deviceaccording to claim 9, wherein at least one of the first substrate andthe second substrate contains a plastic.
 11. A light-emitting deviceaccording to claim 9, wherein the material having the water absorbingproperty contains calcium oxide.
 12. A light-emitting device accordingto claim 9, wherein the display device is incorporated in one selectedfrom the group consisting of a personal computer, a cellular phone, atelevision set, a navigation system, and a lighting system.
 13. Alight-emitting device comprising: a first substrate; a light-emittingelement over the first substrate; a second substrate over thelight-emitting element, wherein the second substrate contains a concaveportion; a sealant between the first substrate and the second substrate;and a material having a water absorbing property formed in the concaveportion, wherein the material having the water absorbing property isprovided so as not to overlap the light-emitting element, so as tosurround a periphery of the light-emitting element, and so as to bespaced from the sealant.
 14. A light-emitting device according to claim13, wherein at least one of the first substrate and the second substratecontains a plastic.
 15. A light-emitting device according to claim 13,wherein the material having the water absorbing property containscalcium oxide.
 16. A light-emitting device according to claim 13,wherein the display device is incorporated in one selected from thegroup consisting of a personal computer, a cellular phone, a televisionset, a navigation system, and a lighting system.